Power output unit and method for delivering constant frequency, constant voltage ac power

ABSTRACT

An accessory unit for use with an engine powered vehicle having a conventional electrical system including a battery, voltage regulator and a dynamo which in normal operation supplies DC power to the vehicle electrical system, including switches adapted to isolate the dynamo from the vehicle electrical system, and means for boosting the DC voltage dynamo output and converting it to a constant frequency AC voltage. An outlet receptacle is provided to accept jacks from power tools, appliances or the like having constant frequency AC voltage power requirements. The outlet receptacle voltage is monitored and the dynamo field current is adjusted in response to variations therein to control the dynamo voltage and amperage input to the unit. In another embodiment of the invention, a secondary coil is provided on the transformer along with conventional rectifying means to step down and rectify the increased AC output voltage. Voltage regulator means is provided to sense variations in this low voltage DC secondary output and control the dynamo field current in response to variations therein to maintain a desired dynamo output voltage and amperage. Additionally, the vehicle battery may be charged by an output from the rectified low voltage secondary output of the transformer.

United StatesPatent Schneider [54] POWER OUTPUT UNIT AND METHOD FORDELIVERING CONSTANT FREQUENCY, CONSTANT VOLTAGE AC POWER [72] Inventor:Franklin R. Schneider, Seattle, Wash.

[73] Assignee: Modern Industries, Incorporated, Seattle,

Wash. [22] Filed: Feb. 8, 1971 [21] Appl. No.: 113,332

[52] U.S.Cl. ..307/10 R, 290/50 [51] lnt.Cl. H02j3/00 [58] FieldofSearch..307/10R;290/l,51,50,38R

[56] References Cited 7 UNITED STATES PATENTS 3,127,518 3/1964 Pruitt..307/10 R X 3,293,443 12/1966 Burch ....307/10RX 3,456,119 7/1969Schneider ....307/10 R X 3,471,706 10/1969 Schneider .,.....307/l0R3,497,709 2/1970 Chilton et a1 ..307/l0 R Primary Examiner-RobertK.Schaefer Assistant Examiner-William J. Smith Attorney-Graybeal, Cole &Barnard 1 1 Apr. 11, 1972 [57] ABSTRACT An accessory unit for use withan engine powered vehicle having a conventional electrical systemincluding a battery, voltage regulator and a dynamo which in nonnaloperation supplies DC power to the vehicle electrical system, includingswitches adapted to isolate the dynamo from the vehicle electricalsystem, and means for boosting the DC voltage dynamo output andconverting it to a constant frequency AC voltage. An outlet receptacleis provided to accept jacks from power tools, appliances or the likehaving constant frequency AC voltage power requirements. The outletreceptacle voltage is monitored and the dynamo field current is adjustedin response to variations therein to control the dynamo voltage andamperage input to the unit.

1n another embodiment of the invention, a secondary coil is- I providedon the transformer along with conventional rectifying means to step downand rectify the increased AC output voltage. Voltage regulator means isprovided to sense variations in this low voltage DC secondary output andcontrol the dynamo field current in response to variations therein tomaintain a desired dynamo output voltage and amperage. Additionally, thevehicle battery may be charged by an output from the rectified lowvoltage secondary output of the transformer.

11 Jim "we Patented April 11, 1972 y j 3,655,991

- I 2 Sheets-Sheet 1 Patented April 11, 1972 3,655,991

2 Sheets-Sheet 2 MIKE/V708 FPA/VA/A/A/P, 5844 5056 WQflM BACKGROUND OFTHE INVENTION 1. Field of the Invention This invention relates to powerunits for use in conjunction with conventional electrical systems ofengines, including the electrical systems of engine powered vehicles, toprovide a constant frequency AC output for operating power tools,appliances or the like. More particularly, this invention relates to apower output accessory unit for use with an engine powered vehicle orthe like, to utilize the DC output of the engine driven dynamo of thevehicle to produce a higher voltage AC power output such as the common120 volts at 60 hertz.

2. Description of the Prior Art As may be well known, the conventionalelectrical systems of engine powered land and marine craft usuallyinclude a DC battery, a dynamo adapted to deliver low voltage DC powerto the vehicle electrical system and a voltage regulator connectedtherebetween and adapted to control the output voltage of the dynamo inresponse to the charge variation of the battery. At present, analternating current generator or alternator is the type dynamo commonlyin use on engine powered vehicles, and conventional altemators include astator having three windings connected to provide a three-phase ACoutput and a rotor with a field winding appropriately driven by theengine. Alternators of this type generally include a rectifying circuitadapted to transform the AC voltage to DC which is then used to powerthe vehicle electrical system and charge the vehicle battery.

It is known to provide auxiliary AC power by modifying the vehicleelectrical system through the addition of a second or piggyback"alternator often mounted adjacent the alternator of the vehicleelectrical system and driven mechanically by belts from the vehicleengine in the same manner as the vehicle electrical system alternator.To produce AC power the AC output of the piggyback alternator isdirectly tapped prior to rectification. AC power sources of this typeare often difficult and expensive to install due to the often crowdedconditions of the vehicle engine compartment, and additionally, sourcesof this type are unsatisfactory in that the AC output voltage, as wellas its frequency, may vary significantly with changes in engine speed,and are therefore not reliable for powering appliances requiringconstant voltage or constant frequency power. So-called overvoltageregulators are sometimes used with AC power sources of this type toprevent high voltage surges which might damage the tools or the likebeing powered, but these devices are unable to prevent the outputvoltage from dropping off.

U.S. Pat. No. 3,174,048 to Snyder et al. discloses an automotive batterycharging circuit of the general type described above wherein the ACoutput of the alternator is employed prior to rectification for limitedpurposes not requiring constant frequency voltage.

U.S. Pat. No. 3,469,072 to Carlson discloses a heater system forprotecting a motor vehicle battery against low temperature which ispowered by the stepped up AC output of the altemator. In Carlson, thealternator is never disconnected from the vehicle electrical system toprovide an increased voltage source.

Zechin U.S. Pat. No. 3,469,073 discloses an auxiliary electrical heatingsystem again powered by the stepped up threephase AC output of thealternator. No means for regulating the output voltage or the frequencyof this voltage is disclosed.

Additionally, power output accessory units are known which boost andtransform the 14 volt DC output of the battery into AC voltage ratherthan boosting the DC alternator output voltage and then transformingthis increased DC voltage to AC, as taught by the instant invention. Theuse of the 14 volt DC battery voltage requires the unit being built tohandle high current loads in the neighborhood of 120 amps or more,thereby necessitating the use of large and relatively expensivecomponents. Further, power units of this type which modify the low DCbattery voltage are generally limited in output to approximately 700watts, unless a special, very high amperage capacity vehicle alternatoris employed therewith.

Further, reference is made to Schneider U.S. Pat. Nos. 3,456,l l9 and3,471,706 which relate to DC power output accessory units wherein theengine dynamo is disconnected from the vehicle battery to increase theDC output voltage of the dynamo.

BRIEF SUMMARY OF THE INVENTION In one form, the present inventionincludes a power output accessory unit adapted to substantially isolatethe alternator of a vehicle electrical system from the rest of theelectrical system, such that the alternator DC output which normallysupplies power to the vehicle electrical system provides a substantiallyincreased voltage. This substantially increased DC voltage isconnectedto the intermediate tap of the primary coil of an autotransformer havinga pair of thyristors and an associated capacitor connected to its endtaps. A constant frequency vibrator or a solid state oscillating circuitis employed to alternately fire the thyristors across the primary coilto produce a constant frequency AC voltage suitable for powering powertools or appliances having constant frequency AC voltage requirements.

While this invention is discussed herein primarily with respect to itsuse in conjunction with a vehicle electrical system, it will beunderstood that it may also be employed in conjunction with engines atfixed locations to provide a constant frequency and voltage power plant.

In another form of the invention a voltage regulator is provided tosense variations in the constant frequency AC voltage and control thefield current of the alternator in response to these variations toprovide a desired increased DC output voltage at the alternator outputtenninal, which in turn is modified to provide a constant AC voltageoutput at the outlet receptacle of the unit.

In still another embodiment the transformer is provided with a secondarywinding which acts to step down the constant frequency AC voltage whichis then rectified and voltage regulated to energize the alternator fieldresponsive to variations in this low voltage DC current, therebyallowing the voltage regulator to be constructed of relativelyinexpensive low voltage components. Further, the secondary coil of thetransformer may be used to perform the additional function ofsimultaneously maintaining the charge of the vehicle battery.

It is thus an object of the present invention to provide a power outputaccessory unit adapted to deliver constant frequency AC voltage foroperating portable power tools, appliances or the like under varying orvarious load power requirements.

Another object of the present invention is to provide a power outputaccessory unit for use on an engine powered land or water craft which iseasy to install and relatively inexpensive to construct.

More particularly, it is an object of the present invention to provide apower output accessory unit able to deliver power at volt AC, 60 hertzat various levels of load power consumption.

Still another object of this invention is to provide a power outputaccessory unit which makes use of the DC output voltage of anenginedynamo to produce AC power.

An additional object of the present invention is to provide an AC poweroutput accessory unit for use in conjunction with the electrical systemof a vehicle adapted to isolate the vehicle alternator from the vehicleelectrical system to allow the DC output voltage of the alternator toincrease.

Still another object of the present invention is to provide an AC poweroutput accessory unit adapted to monitor its power output and controlthe alternator output voltage in response to variations therein.

One more object of the present invention is to provide a power outputaccessory unit able to produce a relatively high power output whilehandling relatively low currents.

An additional object of the present invention is to provide a poweroutput accessory unit for use in conjunction with the electrical systemof a vehicle adapted to simultaneously produce a constant frequency ACoutput and maintain the charge of the vehicle battery.

Other and additional objects and advantages will be apparent from thefollowing description taken in conjunction with the accompany drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front perspective view ofa control panel and outlet receptacle mount of a typical power outputaccessory unit made according to the instant invention.

FIG. 2 is a top plan view of the control panel of FIG. I having the casebroken away and with the various conductors fragmented to more clearlyshow the physical layout of the control panel components.

FIG. 3 is a front perspective view of another typical embodiment of apower output accessory unit made according to the present inventionwherein the control panel, outlet receptacle mount and thecircuitrycontaining case are combined in a single unit.

FIG. 4 is a schematic drawing of the electrical circuitry of a typicalpower output accessory unit made according to the instant invention.

FIG. 5 is a schematic drawing of the electrical circuitry of anotherembodiment of the instant invention.

FIG. 6 is a schematic drawing of a portion of the electrical circuitryof still another embodiment of the instant invention.

DETAILED DESCRIPTION OF THE INVENTION Referring initially to FIGS. 1 and2, the control panel and casing of a typical power output accessory unitis shown which is made according to the instant invention and adapted tobe mounted on or beneath the dashboard of a vehicle by means of pivotalbracket 12. Typical dimensions for this control head would be 3 X 4.5 X8 inches. Cable 14, a portion of which is shown, extends from thecontrol panel and casing to a separate casing (not shown) containing thecircuitry for the unit. The circuitry containing casing may be disposedin the trunk or other storage area of the vehicle so as not to clutterthe passenger compartment, and the circuitry therein is, in turn,connected to the electrical system of the vehicle as will be explainedmore completely hereafter with reference to FIG. 4.

Control panel and casing 10 for a typical power output accessory unitmay include a double pole double throw switch 16 having an on and ofiposition which controls the operation of the power output accessoryunit. Switch 16 may also include a momentary override position for apurpose which will also be described hereafter.

Control panel and casing 10 also mounts a pair of double conductor110-120 volt AC output receptacles 18, which as shown in FIG. 2 maycomprise a single subassembly.

The instant description of a specific embodiment of the presentinvention refers primarily to a power output accessory unit adapted toprovide the common 110-120 volt output at 60 hertz commonly required bypower tools, appliances and the like, from a 12-14 volt engineelectrical system, but it should be understood that, with obviousmodifications, this invention may be employed to produce differentvoltages and/or different design frequencies from engine electricalsystems having like or different voltages. Additionally it should beunderstood that units having rated power outputs varying between 1,200watts and 3,000 watts or higher, for example, may be constructed, byemploying obvious variations in certain unit components.

Circuit breaker means such as fuse 20 in the output receptacle circuit,which in a 2,000 watt unit, for example, would be a may include a 12volt DC storage battery 38 having a 20 amp fuse, as well as indicatorlight 22, voltmeter 24 and ammeter 26 are also mounted on control paneland casing 10. Cable retainer 28 is provided at the rear of casing 10 tosecure electrical conduit 14 extending to the circuitry containingcasing disposed in the vehicle storage compartment or a similarlocation.

FIG. 3 discloses a modified embodiment of the instant invention whereinthe control panel and circuitry containing casing are combined in asingle unit 30. The typical dimensions of this unit would beapproximately 7 X 9 X l2 inches, readily enabling placement of the unitin the vehicle storage compartment min the vehicle passenger compartmentat the option of the owner and depending in part upon the need forplacing outlet receptacles 18 in any particular location. Outletreceptacles, of course, may be disposed at any desired location on theland or water vehicle and connected to outlet receptacles 18 byconventional electrical wiring extension means. The lower portion ofunit 30 includes a control panel having a double pole double throwswitch 16 having a momentary override position, an indicator light 22,circuit breaking fuse 20 and voltmeter 24.- As a matter of choice, noammeter is provided on unit 30, however it will be understood that onecould be provided through obvious rearrangement of the control panel.Cable 32 may extend from unit 30 to the dynamo of the vehicle electricalsystem and to the vehicle battery as will be described more completelyhereafter. Handles 34 are provided on unit 30 to facilitate carrying ofthe unit, while vents 36 aid in dissipating heat generated by thecircuitry contained therein.

Referring now to FIG. 4, the circuitry and operation of one embodimentof the instant power output accessory unit will be described. As'known,a conventional vehicle electrical system grounded negative terminal 40and an ungrounded positive terminal 42; an engine driven alternator 44having a field winding terminal 46, an armature related DC outputterminal 48 and ground 50; and a voltage regulator 52 connected toreceive an input from the battery and additionally connected to thefield winding terminal 46 of the alternator. As has been set forthabove, conventional vehicle electrical system dynarnos supply lowvoltage DC power to the vehicle electrical system and maintain thecharge of battery 38. The conventional alternator is, however, an ACvoltage generator with an internally connected rectifier circuit totransform the altemator generated AC voltage to the DC voltage requiredby the vehicle electrical system. On altemators such as those normallymounted on mass produced vehicles, only the low voltage DC terminals areexposed, and it will thus be understood that terminal 48 relates to theDC output of the alternator.

In normal vehicle operation, and with power output unit switch 16 in theoff position, vehicle ignition switch 54 is closed to set up a chargingcircuit which runs from alternator output terminal 48 through conductor56 to DC ammeter shunt 58, through connector 60 to deenergized contactor62, and then through connector 64 to junction block 66 and back throughconnector 68 to the battery 38. With the ignition switch 54 closed thevehicle voltage regulator controls alternator field 46 through connector70, switch 16. and connector 72 to regulate the battery and vehicleelectrical system voltage.

Dashed line 84 is provided to visually separate the circuitry of theconventional engine electrical system above the line from the circuitryof the power output accessory unit below the line. Dashed square 82 isprovided to indicate, in general, the circuitry of the voltage regulatorof the power output accessory unit itself.

To activate the power output accessory unit to provide power at 1 10-120volt AC, 60 hertz, for example, switch 16 is moved to the on positionshown in dashed line in FIG. 4, thereby isolating the alternator fieldterminal from the control of the vehicle voltage regulator andenergizing the unit. Switch 16 is a double pole double throw contactor,and includes a momentary override portion 86 which is momentarily heldconventional closed to energize contactor 62 through connector 80, fuse78 and connector 76. The momentary portion 86 of switch 16 acts as asafety device to shut the unit down automatically should the vibratorfail to operate or should the 14 volt power supply be lost, thuspreventing potential damage by excessively high alternator current inthe power output accessory unit.

When contactor 62 is energized, it moves, as shown in dashed line, tointerconnect connectors 88 and 90 and deliver the alternator output fromterminal 48 to the center tap 92 of the primary coil 94 ofautotransformer 96 through connector 98 and input fuse 100. In a 2,000watt power unit, for example, it has been found that fuse 100 maysatisfactorily have a 50 amp capacity.

It should be understood that as disclosed herein, the engine whichdrives dynamo 44 is considered to be set at a speed sufficient toproduce the desired increased DC output at dynamo output terminal 48when the dynamo is isolated from the vehicle electrical system. It isalso contemplated that means may be provided to vary this engine speedin response to the electrical load on the unit. For example,a'solidstate control may be used in conjunction with the load responsive,engine speed control components disclosed in Schneider US. Pat. No.3,456,l 19 for this purpose. In one arrangement, the solid state controlis switched on simultaneously with the power output accessory unit bymeans of connector 104A, shown in dotted line. Dotted line connector148A interconnects the solid state control and connector 148 to allowthe control to respond to changes in the field voltage being supplied byvoltage regulator 142. Since field voltage varies with the electricalload being applied at outlet receptacle 18, connector 148 provides adesirable reference to regulate this solid state control. However, otherreference points, such as connectors 122, 124 or 140 could also be used.

Thus this control assembly senses alternator field voltage and respondsto changes therein by varying engine speed to provide the necessaryinput into the power output accessory unit from alternator 44.

When double pole double throw switch 16 is moved to the on position thealternator is isolated from the vehicle electrical system and the DCoutput voltage increases to approximately 60 volts as opposed to the 14volt DC output normally employed to power the vehicle electrical system.This increased approximately 60 volt DC output is fed to the center tapof transformer 96 where it is converted to 60 hertz, 120 volt AC.

Simultaneously with the energization of contactor 62, switch 16 moves toenergize vibrator 102 through connector 104 and a ground through thecoil of the vibrator. In one embodiment of the invention it has beenfound that a 60 cycle vibrator such as'a Model No. 406513 manufacturedby the Oak Manufacturing Company, Crystal Lake, Illinois, issatisfactory, although it is to be understood that other oscillatorymeans, including known solid state oscillating circuits, have equalutility for the purpose.

As disclosed in FIG. 4, the poles 106 and 108 alternately contacted byvibrating reed 110 are connected through resistors 112 and connectors114 and 116 to thyristors, such as silicon controlled rectifiers (SCRs)118 and 120 respectively. Resistors 112 are provided to produce a propergate voltage and current for SCRs 118 and 120. SCR 118 is connected toone end tap of the primary coil 94 of transformer 96, SCR 120 isconnected to the opposite end tap of the primary of the transformer,while capacitor 119 is connected therebetween. The SCR, capacitor andtransformer configuration shown is a so-called McMurray-BedfordInverter, although it will be understood that other similarlyfunctioning circuit configurations may be substituted therefor. In thedisclosed embodiment, as will be understood, vibrator 102 is tuned athertz and SCRs 118 and 120 alternately fire with the 60 volt DCalternator output oscillating across the primary of the transformer. Theoscillation thus induced between the two end taps of the primary coiland across the approximately 60 volt DC input at center tap 92 producesa 120 volt AC voltage across connectors 122 and 124, with connector 122leading to one side of AC receptacle 18 and with connector 124, fuse 20and connector 128 leading to the opposite side of the AC receptacle.

More completely, assuming SCR 118 to be conducting and SCR 120 to beblocking, a condition caused by vibrating reed contacting pole 106,current from the DC alternator output flows through conductor 98 throughthe left side of the transformer primary coil 94. Autotransforrneraction produces a voltage approximately twice the boosted 60 volt outputof the alternator at the anode of SCR 120, which thus charges capacitor119 to approximately volts. When vibrating reed 110 contacts pole 108,SCR 120 is triggered causing the voltage at point 121 to rise, therebyreverse biasing SCR 118 and turning it off. Capacitor 119 maintains thereverse bias for the required turn off time. When SCR 118 is againtriggered by vibrating reed 110, the inverter returns to the firststate. Thus, the DC supply current flows alternately through each sideof the transformer primary producing a 120 volt AC voltage which istapped off to receptacle 18.

While a single receptacle 18 is illustrated in FIG. 5, it will bereadily understood that a two receptacle subassembly such as thatillustrated in FIGS. 1-3 may be readily substituted therefor. Voltmeter24 is connected across AC outlet receptacle 18 to monitor the outputvoltage at the receptacle.

As known, thyristors such as SCRs 118 and 120 once fired remain in aconductive state until turned off, and thus the constant frequency ACoutput voltage generated by alternately firing these devices across theprimary of transformer 96 is fundamentally of the square-wave type. Ifdesired, circuitry can be designed employing transistors of the NPN typewhich may be substituted for SCRs 118 and 120 to produce a substantially sine wave voltage.

FIG. 5 schematically discloses a layout of the circuitry of one simpleform of the instant invention wherein a manual control means such aspotentiometer 130 is provided to allow the alternator field current tobe adjusted in response to changes in the desired 120 volt AC output atoutlet receptacle 18 as monitored by voltmeter 24. The alternator fieldcurrent is adjusted to maintain the DC alternator output voltage in therange of 60 volts which is transmitted to the center tap 92 ofautotransformer 96 through a connector 132 where power at 120 volt AC 60hertz is produced therefrom in substantially the same manner disclosedabove with reference to FIG. 4. Thus it will be understood that, insimple form, the output voltage of the alternator is maintained at alevel substantially higher than the 12-14 volts DC normally needed tocharge the associated battery and power an associated electrical systemand further that this alternator output voltage is maintained byadjustments made in response to variations in the constant frequency ACoutput voltage supplied to outlet receptacle 18.

Referring again to FIG. 4, a secondary coil 134 is shown associated withtransformer 96 to step down the increased voltage at the primary coil.Additionally, rectifiers 136 and 138 are provided to transform the ACvoltage back to DC and thus it will be understood that in FIG. 4,connector 140 is at approximately 14 volts DC.

As has been set forth above, the circuitry within dashed square 82comprises a voltage regulator 142 of the simple transistor typegenerally conventional per se, although diode 144 has been added toblock the battery voltage so that the regulator senses the output of thesecondary of the transformer 96, and diode 146 has been added to limitamperage drain when the switch 16 is in the off position. Low voltage DCline 140 from the secondary 134 of the transformer provides a referencefor the voltage regulator 142 which in turn controls the alternatorfield current through connectors 148, switch 16 and connector 72.Connectors 72 and 148 are interconnected by switch 16 at the time ofinitial actuation of the switch 16 described heretofore. The alternatorfield, and consequently the alternator output, is thus automaticallycontrolled by voltage regulator 142 to produce a substantially constantalternator output voltage sufficient to maintain a constant 120 volt ACvoltage across the primary of transformer 96.

The stepping down and rectifying of the 120 volt AC transformer voltageallows voltage regulator 142 to be constructed of low voltage componentsat relatively low cost as compared to the components of a voltageregulator capable of directly sensing the 120 volt AC output voltage atoutlet receptacle 18 and controlling the alternator field current inresponse to variations in this relatively high AC voltage. It isunderstood however, that a power output accessory unit employing avoltage regulator adapted to monitor the high voltage AC output of thetransformer is also considered to be within the scope of the instantinvention.

Secondary transformer coil 134 and rectifiers 136 and 138 perform anadditional function in that the 14 volt DC voltage produced thereby maybe used to maintain the charge in battery 38 through a circuit includingconnectors 140, 149, diode 144, connector 80, fuse 78, connector 76,connector 64, junction block 66 and connector 68 to battery 38.Ordinarily, a vehicle battery would tend to become depleted if isolatedfrom the alternator output in the manner described above for any lengthof time during engine operation, but the feeding of the 14 volt DCoutput of the secondary coil of the transformer to the battery allowsthe instant power output accessory unit to be operated indefinitelywithout lowering the charge of the battery.

FIG. 6 shows a modified embodiment of autotransformer 96 which may beused in lower wattage power output accessory units and includesadditional end windings 150 and 152 on primary coil 94. As may beunderstood, the provision of these additional end windings allowstransformer 96 to produce the desired 120 volt AC power at outletreceptacle 18 from a lower DC alternator output voltage in line 132.While a principal feature of the present invention, as disclosed withreference to FIGS. 4 and 5, is the use of an increased DC alternatoroutput voltage to produce the desired AC power while handling lowamperage, under low power loads the engine which drives dynamo 44 insuch circumstance runs at unnecessarily high r.p.m. levels. Engine fuelmay be conserved through use of the autotransformer of FIG. 6 which,with the proper number of added end windings, may produce 120 volt ACpower from a DC alternator output of 30 volts, for example. Thus whilethe alternator output voltage is still allowed to increase afterisolation of the alternator from the engine associated electricalsystem, the boosted alternator output level is lower than that disclosedwith reference to FIG. 4. The modification of FIG. 6 may be usedsuccessfully with power units having outputs in the neighborhood of1,200 watts or less wherein the amperage increases due to thelowalternator output voltage are relatively small and do not require theuse of high amperage components, but this modification cannot be used toproduce 2,000 to 3,000 watt or greater outputs, for example, withoutincreasing component capacity.

It will also be understood that the arrangement of FIG. 6 may be usedwith an appropriate number of added end windings and a boosted dynamooutput voltage, and in conjunction with a 240 volt outlet receptacletapped from the outermost additional end windings to provide a poweroutput unit having both a 120 and 240 volt output.

From the above it will be understood that a method is disclosed ofproducing constant frequency AC voltage at an outlet receptacle from anengine having an electrical system including a DC storage battery, anengine driven dynamo having a field winding terminal and an outputterminal normally adapted to deliver low voltage DC power to the engineelectrical system and a voltage regulator receiving a power input fromthe battery and having a field terminal connected to the field windingterminal of the dynamo. This method includes the steps of isolating thedynamo from the engine electrical system and allowing the DC outputvoltage of the dynamo to increase. In the disclosed embodiments of FIGS.4 and 5, the dynamo output voltage is allowed to run up to approximately60 volts DC which is then transformed to 120 volts AC, but it will beunderstood that the dynamo output voltage may be allowed to run up toeither a higher or lower voltage to produce correspondingly higher orlower AC voltages at outlet receptacle l8.

Allowing the dynamo or alternator output voltage to increase allows theuse of components in this power output accessory unit designed to handlerelatively low currents, generally below 50 amps. The use of lowamperage components produces a cost savings when compared to certain ofthe prior art units discussed above which take 14 volts DC off thevehicle battery, and thus, are required to handle currents in the rangeof amps or better.

After isolating the dynamo from the vehicle electrical system andallowing the DC voltage output to increase, this output voltage isconnected to the center tap of the primary coil of an autotransformerhaving a pair of thyristors and an associated capacitor connected to theend taps thereof. A constant frequency vibrator, operating at 60 hertzin the disclosed embodiment, is provided to alternately fire thethyristors across the primary of the autotransformer to produce 120 voltAC 60 hertz output power. Outlet receptacle 18 is connected to theprimary to receive the jacks of tools and appliances having constantfrequency AC power requirements. This AC out put voltage, or in one formof the invention, a stepped down DC voltage, is monitored and thealternator field current is adjusted in response to variations in theunit output voltage to control the alternator or dynamo output voltageat a desired level to produce a constant voltage AC output.

The invention may be embodied in other specific forms without departingfrom the spirit or central characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore to be embraced therein.

What is claimed is:

l. A method of producing constant frequency AC voltage from an engineelectrical system including a DC storage battery; an engine drivendynamo having a field winding terminal and an output terminal whichnormally delivers low voltage DC power to said electrical system; and avoltage regulator receiving a power input from said DC storage battery,and having a field terminal connected to the field winding terminal ofsaid dynamo; said method including the following steps:

a. isolating said dynamo from said electrical system and increasing theDC voltage at the output terminal of the dynamo; applying such increasedvoltage DC output to the primary coil of an autotransformer;

c. oscillating said increased DC voltage across said primary coil at asubstantially constant frequency to produce constant frequency ACvoltage;

monitoring said constant frequency AC voltage; and

e. controlling the field of said dynamo in response to variations in thevoltage level of said constant frequency AC voltage to maintain asubstantially constant AC voltage level at said dynamo outlet terminal.

. The method of claim 1 including the steps of: stepping down andrectifying a portion of said constant frequency AC voltage;

. monitoring said stepped down DC voltage; and

controlling the field of said dynamo in response to variations in saidstepped down DC voltage to maintain a desired increased voltage at saiddynamo outlet terminal.

. The method of claim 1 including the steps of:

stepping down and rectifying a portion of said constant frequency ACvoltage to produce a DC voltage having a value of approximately 14volts; and

b. maintaining the charge of said DC storage battery of said engineelectrical system by applying said stepped down DC voltage thereto.

pro

4. A power output unit adapted to produce constant frequency AC voltagefor use with an engine of the type having an electrical system includinga dynamo, a DC battery and a voltage regulator, including:

switch means movable to isolate said dynamo from said electrical systemand enabling the dynamo DC output voltage to increase;

means for converting the increased DC output voltage from said dynamo toa constant frequency AC voltage;

means sensing the level of said constant frequency AC voltage; and

means for controlling said dynamo DC output voltage to maintain said DCoutput voltage at a relatively constant level. 5. The power output unitof claim 4 wherein said means for transforming a DC output voltage fromsaid dynamo to a higher, constant frequency AC voltage includesautotransformer means, and means for oscillating said DC output voltageacross the primary coil of said autotransformer means.

6. The power output unit of claim 5 wherein said means for oscillatingsaid DC output voltage includes a pair of thyristors connected to theend taps of the autotransformer coil, capacitor means connected betweensaid thyristors, and a constant frequency vibrating means adapted toalternately fire said thyristors.

7. The power output unit of claim 6 wherein said vibrating meansincludes a solid state oscillating circuit.

8. The power output unit of claim 4 wherein the means for controllingsaid dynamo DC output voltage is responsive to variations in theconstant frequency AC voltage.

9. The power output unit of claim 8 comprising voltage regulator meansresponsive to variations in the AC voltage and providing a signal outputconnected to control the dynamo DC output voltage.

10. The power output unit of claim 4 including means for stepping downand rectifying said constant frequency AC volt age, means for monitoringsaid stepped down DC voltage; and means for controlling said dynamo DCoutput voltage responsive to variations in said stepped down DC voltage.

11. The power output unit of claim 10 wherein said means for steppingdown and rectifying said constant frequency AC voltage includes anautotransformer having a secondary step down coil and rectifier meansconnected to said secondary coil and providing a DC output responsive tovariations in the level of the constant frequency AC voltage.

12. A power output unit for use with an engine of the type having anelectrical system including a DC storage battery; an engine drivendynamo having a field winding terminal an an output terminal whichnormally delivers low voltage DC power to said electrical system; and avoltage regulator receiving a power input from said DC storage battery,and having a field terminal connected to the field winding terminal ofsaid dynamo; said power output accessory unit being designed to providea power output for operating power tools, appliances or the like havinga constant frequency AC voltage requirement, and comprising:

switch means adapted to disconnect said dynamo from said engineelectrical system and allow the DC voltage at the output terminal ofsaid dynamo to increase;

autotransformer means connected to the output of said dynamo;

means oscillating said increased DC dynamo voltage across saidautotransformer means and producing a constant frequency AC voltage;

AC outlet receptacle means connected across said autotransformer coil;

means monitoring the output voltage of said autotransformer; and

means controlling the dynamo field current in response to variations insaid autotransformer output to maintain a desired voltage level ofconstant frequency AC voltage at said outlet receptacle.

13. The power output unit of claim 12 wherein said means monitoring theoutput voltage of said autotransformer and said means controlling saiddynamo field current include a voltage regulator.

14. The power output unit of claim 12 including a secondary winding onsaid autotransformer means adapted to step down the AC voltage, andrectifier means converting the stepped down output of said secondarywinding to a DC voltage, and means applying said DC voltage as the inputto said voltage regulator.

15. The power output unit of claim 14, comprising means applying anoutput of said voltage regulator to the field winding of said dynamo tomaintain the constant frequency AC voltage at said outlet receptacle ata desired voltage level.

16. The power output unit of claim 12 wherein said switch means includesa momentary portion adapted to automatically disconnect said poweroutput accessory unit from said engine electrical system in response tothe failure of said unit and thereby prevent the application of highvoltage and/or high amperage from the dynamo to said power outputaccessory unit.

17. A power output unit for use with an engine of the type having anelectrical system including a DC storage battery; an engine drivendynamo having a field winding terminal and an output terminal whichnormally delivers low voltage DC power to said electrical system; and avoltage regulator receiving a power input from said DC storage battery,and having a field terminal connected to the field winding terminal ofsaid dynamo; said power output accessory unit being designed to providea power output for operating power tools, appliances or the like havinga constant frequency AC voltage requirement, and comprising:

switch means adapted to disconnect said dynamo from said vehicleelectrical system; autotransformer means connected to the output of saiddynamo;

means oscillating said increased DC dynamo voltage across saidautotransformer means and producing a constant frequency AC voltage;

AC outlet receptacle means connected across said autotransformer coil;

means monitoring the output voltage of said autotransformer; and

means controlling the dynamo field current in response to variations insaid autotransformer output to maintain a desired voltage level ofconstant frequency AC voltage at said outlet receptacle.

18. The power output unit of claim 17 wherein said means monitoring theoutput voltage of said autotransformer and said means controlling saiddynamo field current include a voltage regulator.

19. The power output unit of claim 17 including a secondary winding onsaid autotransformer means adapted to step down the AC voltage, andrectifier means converting the stepped down output of said secondarywinding to a DC voltage, and means applying said DC voltage as the inputto said voltage regulator.

20. The power output unit of claim 19 comprising means applying anoutput of said voltage regulator to the field winding of said dynamo tomaintain the constant frequency AC voltage at said outlet receptacle ata desired voltage level.

21. A power output unit for use with an engine powered vehicle of thetype having an electrical system including a DC storage battery; anengine driven dynamo having a field winding terminal and an outputterminal which normally delivers low voltage DC power to the vehicleelectrical system; and a voltage regulator receiving a power input fromsaid DC storage battery, and having a field terminal connected to thefield winding terminal of said dynamo; said power output accessory unitbeing designed to provide a power output at the vehicle for operatingpower tools, appliances or the like having a constant frequency,constant voltage, power requirement, and comprising:

switch means adapted to disconnect said dynamo from said vehicleelectrical system and allowing the voltage at the output terminal ofsaid dynamo to increase; autotransformer means including a primary coilconnected to said dynamo output terminal;

fixed frequency oscillator means applying said increased DC dynamovoltage across said primary coil to produce a constant frequency ACvoltage;

double conductor AC outlet receptacle means connected across saidprimary coil and adapted to receive power plugs from power tools,appliances or the like having a constant frequency AC voltagerequirement;

secondary coil means associated with said autotransformer means betweensaid rectified transformer secondary coil output and said battery tomaintain said vehicle battery in a charged condition.

UNITED STATES PATENT OFFICE CERTWECATE OF CORREQTION Patent No. 3 655991 Dated April 11 1972 Inventor(s) FRANKLIN R SCHNEIDER It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 8 at line 60 change "AC" to DC Signed and sealed this 27th day ofNovember 1973.

(SEAL) Attest'.

EDWARD MJLETGHERJR. RENE Di. TEG'IMEYER I Attesting Officer ActingGommissioner of Patents I FORM PO-10 50 (10-69) U$COMM-DC 803764 69 1:us. GOVERNMENY PRINTING OFFICE: I969 0-356-334,

UNITED STATES PATENT OFFEGE QERTWECATE OF CORREUNN Patent No. 3 655 991D d April 11 1972 Inventofls) FRANKLIN R. SCHNEIDER It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 8, at line 60, change "AC" to DC Signed and sealed this 27th dayof November 1973.

(SEAL) Attest: v

EDWARD M.+FI.1ETGHER,JB; D a momma Attesting Officer Y ActingCiommissioner of Patents FORM PC3-1050 10-69) U S COMM-DC scam-P69 9U.5. GOVERNMENT PRINTING OFFKIEI I969 O-3 66-334,

1. A method of producing constant frequency AC voltage from an engineelectrical system including a DC storage battery; an engine drivendynamo having a field winding terminal and an output terminal whichnormally delivers low voltage DC power to said electrical system; and avoltage regulator receiving a power input from said DC storage battery,and having a field terminal connected to the field winding terminal ofsaid dynamo; said method including the following steps: a. isolatingsaid dynamo from said electrical system and increasing the DC voltage atthe output terminal of the dynamo; b. applying such increased voltage DCoutput to the primary coil of an autotransformer; c. oscillating saidincreased DC voltage across said primary coil at a substantiallyconstant frequency to produce constant frequency AC voltage; d.monitoring said constant frequency AC voltage; and e. controlling thefield of said dynamo in response to variations in the voltage level ofsaid constant frequency AC voltage to maintain a substantially constantAC voltage level at said dynamo outlet terminal.
 2. The method of claim1 including the steps of: a. stepping down and rectifying a portion ofsaid constant frequency AC voltage; b. monitoring said stepped down DCvoltage; and c. controlling the field of said dynamo in response tovariations in said stepped down DC voltage to maintain a desiredincreased voltage at said dynamo outlet terminal.
 3. The method of claim1 including the steps of: a. stepping down and rectifying a portion ofsaid constant frequency AC voltage to produce a DC voltage having avalue of approximately 14 volts; and b. maintaining the charge of saidDC storage battery of said engine electrical system by applying saidstepped down DC voltage thereto.
 4. A power output unit adapted toproduce constant frequency AC voltage for use with an engine of the typehaving an electrical system including a dynamo, a DC battery and avoltage regulator, including: switch means movable to isolate saiddynamo from said electrical system and enabling the dynamo DC outputvoltage to increase; means for converting the increased DC outputvoltage from said dynamo to a constant frequency AC voltage; meanssensing the level of said constant frequency AC voltage; and means forcontrolling said dynamo DC output voltage to maintain said DC outputvoltage at a relatively constant level.
 5. The power output unit ofclaim 4 wherein said means for transforming a DC output voltage fromsaid dynamo to a higher, constant frequency AC voltage includesautotransformer means, and means for oscillating said DC output voltageacross the primary coil of said autotransformer means.
 6. The poweroutput unit of claim 5 wherein said means for oscillating said DC outputvoltage includes a pair of thyristors connected to the end taps of theautotransformer coil, capacitor means connected between said thyristors,and a constant frequency vibrating means adapted to alternately firesaid thyristors.
 7. The power output unit of claim 6 wherein saidvibrating means includes a solid state oscillating circuit.
 8. The poweroutput unit of claim 4 wherein the means for controlling said dynamo DCoutput voltage is responsive to variations in the constant frequency ACvoltage.
 9. The power output unit of claim 8 comprising voltageregulator means responsive to variations in the AC voltage and providinga signal output connected to control the dynamo DC output voltage. 10.The power output unit of claim 4 including means for stepping down andrectifying said constant frequency AC voltage, means for monitoring saidstepped down DC voltage; and means for controlling said dynamo DC outputvoltage responsive to variations in said stepped down DC voltage. 11.The power output unit of claim 10 wherein said means for stepping downand rectifying said constant frequency AC voltage includes anautotransformer having a secondary step down coil and rectifier meansconnected to said secondary coil and providing a DC output responsive tovariations in the level of the constant frequency AC voltage.
 12. Apower output unit for use with an engine of the type having anelectrical system including a DC storage battery; an engine drivendynamo having a field winding terminal an an output terminal whichnormally delivers low voltage DC power to said electrical system; and avoltage regulator receiving a power input from said DC storage battery,and having a field terminal connected to the field winding terminal ofsaid dynamo; said power output accessory unit being designed to providea power output for operating power tools, appliances or the like havinga constant frequency AC voltage requirement, and comprising: switchmeans adapted to disconnect said dynamo from said engine electricalsystem and allow the DC voltage at the output terminal of said dynamo toincrease; autotransformer means connected to the output of said dynamo;means oscillating said increased DC dynamo voltage across saidautotransformer means and producing a constant frequency AC voltage; ACoutlet receptacle means connected across said autotransformer coil;means monitoring the output voltage of said autotransformer; and meanscontrolling the dynamo field current in response to variations in saidautotransformer output to maintain a desired voltage level of constantfrequency AC voltage at said outlet receptacle.
 13. The power outputunit of claim 12 wherein said means monitoring the output voltage ofsaid autotransformer and said means controlling said dynamo fieldcurrent include a voltage regulator.
 14. The power output unit of claim12 including a secondary winding on said autotransformer means adaptedto step down the AC voltage, and rectifier means converting the steppeddown output of said secondary winding to a DC voltage, and meansapplying said DC voltage as the input to said voltage regulator.
 15. Thepower output unit of claim 14 comprising means applying an output ofsaid voltage regulator to the field winding of said dynamo to maintainthe constant frequency AC voltage at said outlet receptacle at a desiredvoltage level.
 16. The power output unit of claim 12 wherein said switchmeans includes a momentary portion adapted to automatically disconnectsaid power output accessory unit from said engine electrical system inresponse to the failure of said unit and thereby prevent the applicationof high voltage and/or high amperAge from the dynamo to said poweroutput accessory unit.
 17. A power output unit for use with an engine ofthe type having an electrical system including a DC storage battery; anengine driven dynamo having a field winding terminal and an outputterminal which normally delivers low voltage DC power to said electricalsystem; and a voltage regulator receiving a power input from said DCstorage battery, and having a field terminal connected to the fieldwinding terminal of said dynamo; said power output accessory unit beingdesigned to provide a power output for operating power tools, appliancesor the like having a constant frequency AC voltage requirement, andcomprising: switch means adapted to disconnect said dynamo from saidvehicle electrical system; autotransformer means connected to the outputof said dynamo; means oscillating said increased DC dynamo voltageacross said autotransformer means and producing a constant frequency ACvoltage; AC outlet receptacle means connected across saidautotransformer coil; means monitoring the output voltage of saidautotransformer; and means controlling the dynamo field current inresponse to variations in said autotransformer output to maintain adesired voltage level of constant frequency AC voltage at said outletreceptacle.
 18. The power output unit of claim 17 wherein said meansmonitoring the output voltage of said autotransformer and said meanscontrolling said dynamo field current include a voltage regulator. 19.The power output unit of claim 17 including a secondary winding on saidautotransformer means adapted to step down the AC voltage, and rectifiermeans converting the stepped down output of said secondary winding to aDC voltage, and means applying said DC voltage as the input to saidvoltage regulator.
 20. The power output unit of claim 19 comprisingmeans applying an output of said voltage regulator to the field windingof said dynamo to maintain the constant frequency AC voltage at saidoutlet receptacle at a desired voltage level.
 21. A power output unitfor use with an engine powered vehicle of the type having an electricalsystem including a DC storage battery; an engine driven dynamo having afield winding terminal and an output terminal which normally deliverslow voltage DC power to the vehicle electrical system; and a voltageregulator receiving a power input from said DC storage battery, andhaving a field terminal connected to the field winding terminal of saiddynamo; said power output accessory unit being designed to provide apower output at the vehicle for operating power tools, appliances or thelike having a constant frequency, constant voltage, power requirement,and comprising: switch means adapted to disconnect said dynamo from saidvehicle electrical system and allowing the voltage at the outputterminal of said dynamo to increase; autotransformer means including aprimary coil connected to said dynamo output terminal; fixed frequencyoscillator means applying said increased DC dynamo voltage across saidprimary coil to produce a constant frequency AC voltage; doubleconductor AC outlet receptacle means connected across said primary coiland adapted to receive power plugs from power tools, appliances or thelike having a constant frequency AC voltage requirement; secondary coilmeans associated with said autotransformer and adapted to step down thevoltage across said primary coil; rectifier means associated with theoutput of said secondary coil; voltage regulation means connectedbetween the rectified, secondary coil output and said dynamo fieldterminal and adapted to control said dynamo field current in response tovariations in the secondary coil output.
 22. The power output unit ofclaim 14 including connector means between said rectified transformersecondary coil output and said battery to maintain said vehicle batteryin a charged condition.